A field experiment was carried out to determine the critical period of weed interference in corn, under a no-tillage system, based on the phenological stage of corn crop growth, at the Gralha Azul Experimental Farm/PUC PR - Brazil, during the growing season of 2000/2001. The experimental design was a randomized complete block arranged in a 2x7 factorial, with four replications. The fourteen treatments evaluated resulted from two series of treatments: with the crop weed free during the initial crop development and with the crop weedy during the initial crop development, in five phenological stages of corn crop growth: V2, V4, V6, V8 and V10 and two checks. The experiment was carried out on an area under no-till system. Seeding, fertilization, and insect and disease control were conducted according to crop technology. Weed interference critical period was between V2 and V7 phenological stages of growth, and corn yield was reduced in 87% when the crop was kept weedy during all the cycle, compared to the weed free crop. The dicotyledon species represented 22.3% of the community, with Taraxacum officinale, Senecio brasiliensis, Rumex obtusifolius and Bidens pilosa being most prevalent. Monocotyledons species represented 77.7%, and Brachiaria plantaginea was the most prevalent. Biomass accumulation of corn, final population and ear per plant were not affected by weed interference.
corn; phenology; interference; critical period; no-till
